Refining of hydrocarbon distillates



R. c. ARNOLD ET AL 2,739,925 REFINING OF HYDROCARBON DISTILLATES March 27, 1956 C IIIIII l Mm Filed Oct. 24, 1951 a M. R N m mm m r. MAL g "H A m p rm wn RA 739,925 Patented Mar. 27, 1956 2,739,925 REFINING OF HYDROCARBON DISTILLATES Robert C. Arnold, Park Forest, IlL, and Arthur P. Lien, Highland, IntL, assignors to Standard Oil Company, Chicago, 11]., a corporation of Indiana Application October 24, 1951, Serial No. 252,912 7 Claims. (Cl. 196-30) Practically all hydrocarbon oils derived from natural sources consist of paraflins, naphthenes, aromatics, organic sulfur compounds and some organic nitrogen and oxygen compounds. For some purposes the presence of aromatics is desirable, e. g., gasolines and high solvency naphthas. For other uses the presence of large amounts of aromatics is objectionable, e. g, burning oils and domestic fuel oils. For most common uses of hydrocarbon oils the presence of organic sulfur compounds is objectionable even though small amounts are tolerated. The

magnitude of the problem is illustrated by the fact that heater oil obtained from West Texas crude contains about of aromatic hydrocarbons and about 4% of organic sulfur compounds-its total sulfur content being about 0.7 wt. percent. Sulfur contents up to about 1.5% are not uncommon.

A very large number of processes for reducing sulfur and aromatic content of hydrocarbon distillates have been developed such as sulfuric acid treating, silica gel extraction, liquid S02 extraction, liquid HF extraction, etc. Liquid HF extraction removes organic sulfur compounds and some of the polynuclear aromatic compounds. Liquid S02 extraction removes aromatic hydrocarbons and organic sulfur compounds, but the selectivity for the sulfur compounds is so low that in order to produce an acceptable low-sulfur oil, it is necessary to take a prohibitive loss of the feed stock to extract.

An object of our invention is to refine hydrocarbon distillates by substantially reducing the amount of both organic sulfur compounds and aromatic compounds present therein. Another object is to produce a domestic fuel oil of good burning quality and odor by removing organic sulfur compounds and aromatic compounds therefrom.

We have found that a low-sulfur oil of good burning quality can be obtained from a high-sulfur, high-aromatic content distillate without excessive treating loss by contacting said distillate at a temperature below about 10 C. with a treating agent consisting of an aluminum chloride-hydrocarbon complex and sufiicient liquid sulfur dioxide to obtain a two-phase separation wherein the extract phase consists of liquid S02, AlCls complex and extract materials.

It is well known that substantially anhydrous AlCls will form an adduct with many organic compounds, particularly olefinic and aromatic hydrocarbons. These adducts are commonly referred to as complexes. Many well known processes use an AlCh-hydrocarbon complex Ind as a catalytic agent in carrying out chemical reactions such as alkylation, polmerization, isomerization, cracking, etc. The complex formed by the reaction of AlCls and a hydrocarbon such as olefin, aromatic, paraflin or naphthene may contain from about 25 to about wt. percent of AlCls. In some cases the amount of AlCls is increased above the stoichiometric amount by dissolving additional amounts of AlCl3 in the complex. In general these complexes are clear, mobile liquids ranging in color from yellow to red.

A complex when used as a catalyst for hydrocarbon conversions gradually loses its activity and becomes spent. Usually as the activity of the complex declines, the hydrocarbon content of the complex increases. However, a. complex that is spent for one type of reaction may be active for catalyzing a different type of reaction, e. g., a spent alkylation complex can be used to catalyze polymerization of isobutylene.

It is known that AlCls-hydrocarbon complexes have a selective solvent action for the naphthenic and the aroma tic constituents of lubricating oil fractions. However, we have found that the complex has relatively little effectiveness in desulfurizing hydrocarbon distillates and in particular those distillates in the heavier-than-gasoline range, such as, heater oil and kerosene. We have discovered that a treating agent consisting of an AlCls-hydrocarbon complex and liquid S02 will give a greater degree of desulfurization of a petroleum distillate than will the sum of the desulfurization effects of either of the two treating agents alone. Furthermore, we have discovered that not only will a freshly prepared complex in combination with liquid S02 produce an effective amount of desulfurization, but also partially spent complexes, or those which are completely spent for some particular catalytic purpose, will produce an effective amount of desulfurization when used in combination with liquid S02.

The Alcls-hydrocarbon complex can be prepared by contacting substantially anhydrous AlCl3, preferably in the presence of hydrogen chloride, with various hydrocarbons; for example, olefins, such as isobutylene; certain parafiins, such as isooctane; aromatics; or mixtures of these hydrocarbons. The complex should contain in excess of 25 wt. percent of AlCls and preferably in excess of about 50% of AlCl3. While freshly prepared complex can be used in our process, we prefer to operate with a spent complex obtained from some other process using a complex as a catalyst; the spent complex should contain preferably between 50 and 75 wt. percent AlCls.

Some desulfurization can be obtained by using as little as 0.5 "gram mol of AlCls, in the form of an AlCla-hydrocarbon complex, per gram atom of sulfur present in the raw oil. Virtually complete desulfurization is obtainable for oils of sulfur content up to about 1.5 wt. percent by using between 3 and 5 or more mols of AlCls per gram atom of sulfur present in the raw oil. (Hereafter it is to be understood that the term mols of A1013 refers to gram mols of AlCls present in an AlCla-hydrocarbon complex per gram atom of sulfur in the raw oil.) Normally a sufficiently low sulfur product oil can be obtained by using from about 1 to about 3 mols of AlCls.

We have found that the burning quality of a high-sulfur, high-aromatic heater oil is markedly improved by the removal of even a small amount of aromatic compounds when using a treating agent consisting of an AlCls-hydrocarbon complex and liquid S02. Considerable improvement in burning quality is obtained when using only enough liquid S02 to obtain a two-phase separation of rafiinate oil and extract phase. The minimum amount of liquid S02 needed is about that amount soluble in the raw oil in the absence of complex. For example, at a treating temperature of about 35 C.,

about 14 volume percent of liquid S02 is soluble in a West Texas heater oil. However, some improvement in desulfurization and burning quality is obtainable when using even smaller amounts of liquid 30: since. an $02.- rich phase appears when the complex is. added; to a saturated solution of S02 and oil. At a fixed. complex. usage the extent of desulfurization increases markedly with in crease in liquidlSOz usage up to about 25'volume percent based on raw oil; above this point the gain: in desulfuri'zation per unit of additional S02 usage is small, and about 100 volume percent is about the maximum desirable amount of liquid S02. In some cases. where not. only maximum desulfurization but also. maximum. dearomatization is desired, the liquid SOz usage. may be as much as 500 volume percent. In. general, we prefer to. use. from at least enough liquid S02 to exceed the. solubility of S02 in the raw oil and preferably about 25%. to. about 100' volume percent of liquid S02. based on raw oil..

The effectiveness of the liquid SOz-AlCls complex treating agent is substantially independentof temperature below about C. Above 0 C. the etlectiueness of the treating agent decreases rapidly, and about 101 C.. is. the highest temperature at which reasonable effectiveness can be maintained. In addition to the eflect on desulfurization and dearomatization, temperature has an eflect on the color of the final oil. At temperatures of about C. and below, final oils of substantially water white color are obtainable. The color of the product oil darkens markedly as the temperature of contacting. increases until at about 0 C. the product. oil. is no better in color than the raw oil. We prefer to operate our process at temperatures below about 0 C. and. preferably below about -20 C.

The time of contacting of the treating agent and the raw oil is dependent upon the intimacy of the contacting and also somewhat upon the contacting temperature. Ordinarily the contacting time will be between about /2' minute and 60 minutes; usually about 5 minutes will be sufiicient.

When the raw distillate is very viscous or of high pour point, it may be desirable to dilute the feed with a low boiling hydrocarbon, such as butane, pentane, hexane, petroleum ether, etc. The diluent should be inactive toward the treating agent.

Our refining process can be used for various petroleum feed stocks, such as naphthas, kerosenes, heater oiIs,. gas oils and lube oils. It is of particular use in treating distillates in the heavier-than-gasoline boiling range, i. e., 300 to 650 F. Our process can be used not only on virgin stocks, but also on oils obtained from various conversion processes, e. g., thermal cracking and. coking,

catalytic cracking, products of other solvent extraction processes, etc. The high olefin content of thermally cracked oils interferes somewhat with the phase se ration in our process even though these oils can be use therein. catalytically cracked oils are particularly suitable for treatment by our process because they contain large amounts of refractory sulfur compounds and aromatic compounds. In general any hydrocarbon oil containing excessive amounts of organic sulfur compounds is a suitable feed for our process.

The product oil from our process is an excellent feed to a catalytic cracking operation because of its very low sulfur content and low aromatic content. In some cases our process can be used for the sole purpose ofupgrading undesirable stocks and making them suitable for use in the catalytic cracking operation.

The extract phase from our process consists of liquid S02, AlCl3 complex, organic sulfur compounds and hydrocarbons. The organic sulfur compounds and hydrocarbons can be recovered from the extract phase by removing the S03 and hydrolyzing the complex with water or preferably a dilute hydrochloric acid solution; The extract oil obtained by the decomposition of the extract phase is very highin sulfur content and may contain from 4 to 8% sulfur. Another method of treatment of the extract phase is to remove the S02 and then to distill some of the hydrocarbons and sulfur compounds away from the complex; in this method of operation the temperature of the SOs-free material should be maintained at less than about 400 to 500 F. in order to avoid excessive cracking of the materials and coke formation in the vessel. The amount of cracking may be reduced by carrying. out this operation under vacuum. By this procedure it is possible to recover a substantial percentage of hydrocar-bons containing less sulfur than the sulfur content of the total extract oils.

We have found that removal of a portion of the S02 from; the. extract phase results ina, two-phase separation of a second rafiinate phase and a second extract phase. The second rafiinate phase consists of mainly aromatic hydrocarbons; the hydrocarbons in the second raflinate phase have a sulfur content muchlower thanthe sulfur content of. the total extract oil, and. in some. cases less than 1%.. The second extract oil obtained by removing the=remainingSO. ;and by hydrolyzing' the- MCI; complex consists mainly of organic sulfur compounds containing in-some cases as much as 12% sulfur.

We have found that. the second rafiinate oil is; an excellent feed to a catalytic cracking operation. When this. oil. is catalytically cracked, a veryhigh yield of high octane number naphtha. is obtained; and this: naphtha has a remarkably low sulfur content, in some cases less than 005%.

Also; we: have found. that when a maximum yield of low sulfur product oil is desired without regard to dearematizatio-n, the yield of the product oil can be. markedly increased without substantial increase in sulfur content by recycling. the second raflinate oil to the initial contaeting step.

Thev following data are given to illustrate the, results obtainable by our process. The feed stock ineach instance. was avirgin West Texas heater oil with. thefollowingicharacteristics:

'API 40.9 Sulfur (wt. percent) 0.6.1 n 1,4558 filolor, Saybolt +13 ASTM distillation:

IBP FL- 330 50% FL- 450 Max FL- 555 of S02... The extract phase was decomposed by removing the S02 and hydrolyzing the substantially SOz-free. material with cold water. For purposes of comparison, runs were made with liquid S02 alone and with AlCla-hydrocarboncomplex alone containing 65 wt. AlCls, which complex was. obtained by reacting AlCIs and isooctane. Two. tools. of A1013. per gram atom of sulfur in the feed were used. Lastly, the. oil was treated with. the same amount of liquid S02 and complex together as used in Runs 1- and 2..

The percent desulfurization obtainable in the absence of the synergistic elfect of our treating agent would have been about 51% In order to more fully describe a specific embodiment of our invention, reference is made to the accompanying drawing which constitutes a part of this specification and in which a schematic flow diagram of our process is shown.

The feed stock, for example, a virgin heater oil distillate from a West Texas crude, from source 11, is passed through line 12 into a drying zone wherein it is substantially dehydrated. The presence of water in the treating system is extremely undesirable because water reacts with the AlCls-hydrocarbon complex and also water increases the corrosive tendencies of liquid S02. Drying zone 13 comprises conventional equipment, such as, a vessel packed with calcium chloride, alumina, or the like.

The dried distillate is passed through line 14 into deaeration zone 16, wherein air dissolved or entrained in the feed is substantially removed. Conventional equipment such as is ordinarily employed in commercial processes of liquid S02 refining of hydrocarbon oils may be employed in zone 16. The dried, deaerated distillate is passed through line 17 into heat exchanger 18, wherein the temperature of the feed is lowered to the desired treating temperature; herein we operate at -20 C.

In the case of very viscous distillates, the viscosity can be reduced by dilution with a hydrocarbon oil that is inert to the treating agent. Suitable diluents are butane, pentane, petroleum ether, etc. The diluent, from source 21, may be introduced by way of valved line 22 into line 17.

The dried, deaerated (diluted) distillate is introduced by way of line 19 into the lower portion of extraction tower 26. Tower 26 may be packed with corrosion resistant materials, such as Raschig rings or Berl saddles, or may be of modified bubble cap type construction. Instead of a tower, we can use a series of batch countercurrent vessels. In tower 26, the feed is contacted with a treating agent consisting of liquid S02 and an AlClshydrocarbon complex, which complex contains about 60 wt. percent of AlCl3. Although the liquid S02 and the complex can be added to tower 26 as separate streams, we prefer to combine them and introduce the mixture into the tower. 1

In this example, liquid S02, 50 volume percent based on distillate, from source 28 is passed through lines 29 and 31 into mixer 32. The AlCla-hydrocarbon complex, 2 gram mols of A1013 per gram atom of sulfur in the feed distillate, from source 33 is passed through line 34 into mixer 32, where the complex and the liquid S02 are cornmingled. From mixer 32 the treating agent passes by way of line 36 and into tower 26 through any one or all of valved manifold lines 37, 38 and 39.

The temperature in tower 26 is maintained in this example at about -20 C. Sufiicient pressure is maintained on the system to keep the S02 liquid, even though the temperature of contacting may be above the boiling point of liquid S02, i. e., l C. at 15 p. s. i. a. The contacting period in tower 26, in this example, is minutes.

The rafiinate phase, consisting of hydrocarbon and some S02 dissolved therein, passes out of tower 26 by way of line 46 to stripper 47. In stripper 47, the S02 is driven oif by raising the temperature of the raflinate phase to about 200 F. by means of internal heater 48. The S02 passes out of stripper 47 through line 49. The low sulfur product oil passes out of stripper 47 through line 51 to storage, not shown.

The extract phase, consisting of liquid S02, AlCls complex, organic-sulfur compounds and hydrocarbons, passes out of tower 26 through line 54, through heat exchanger 56 and through line 5'7 into a vessel 58. The extract phase is heated so that a portion of the S02 will be flashed as the extract phase enters vessel 58. Vessel 58 is provided with a pancake coil 59 which serves to condense any hydrocarbons that may be vaporized along with the S02 so that only S02 passes out of vessel 58 by way of line 61. Sufficient S02 must be removed to cause the formation of two phases; in this example we remove about one-half the S02 from the extract phase by means of the flashing operation in vessel 58.

The bottoms from vessel 58 are passed through line 64 into a settler 66. In settler 66 there exists a second rafdnate phase consisting of some S02, hydrocarbonsmainly aromatics, and some organic-sulfur compounds; also present is a second extract phase consisting of liquid S02, complex, organic-sulfur compounds and some hydrocarbons. From settler 66, the second raffinate phase is passed through lines 68 and 69 into stripper 71.

In stripper 71, the S02 is removed by heating the raffinate to about 200 F. by means of internal heater 72; the S02 passes out through line 73. The bottoms from stripper 71 consist mainly of aromatic hydrocarbons, some non-aromatic hydrocarbons, and some organic-sulfur compounds. In general, the sulfur content of the second raffinate oil is considerably less than the sulfur content of the total extract oil. The second rafiinate oil-low sulfur extractpasses to storage by way of line 74.

In some cases, maximum yield of low sulfur product may be the object of the treatment. This object can be attained by recycling the second raffinate phase from settler 66 by way of line 68 and 76 to a lower part of tower 26. By this method of operation, the yield of product oil from stripper 47 is increased with substantially no increase in sulfur content over the no-recycle operation.

The second extract phase from settler 66 is passed through line 81 into stripper 82. Substantially all the S02 is removed by heating the extract phase to between about 150 and 250 F. under a pressure that permits vaporization of the S02 alone, i. e., between about 25 and p. s. i. a., by means of internal heater 83. The temperature in the bottom of stripper 82 should be maintained as low as possible in order to reduce the cracking of both hydrocarbons and sulfur compounds. The vapors from stripper 82 pass out through line 84.

The essentially SOz-free bottoms in stripper 82 pass out by way of line 86 to mixing vessel 87. Dilute aqueous HCl, for example, 10%, from source 91 is passed through lines 92 and 93 into mixer 87. The AlCla-containing bottoms are decomposed by the aqueous I-lCl to form a hydrocarbon and organic-sulfur compound oil and an aqueous solution of A1013 reaction product. We could use water for the decomposition but prefer to use aqueous HCl because the reaction is not as vigorous, and because aqueous HCl prevents formation of gelatinous aluminum hydroxide. Mixer 87 should be provided with a cooling coil, not shown, if water is to be used to decompose the AlCla-containing extract.

The mixture from vessel 87 is passed through line 96 into settler 97 Where a high sulfur extract layer and an aqueous layer separate. From settler 97 there is vented through line 98 a stream of H28, S02 Water vapor and minor amounts of HCl, which materials were released in the decomposition procedure. The high sulfur extract, consisting mainly of organic-sulfur compounds, is sent to storage or to further treatment by Way of line 99. The aqueous solution is sent to waste disposal by way of line 101.

Usually the streams in lines 84 and 98 contain some water, which water must be removed in order to permit reuse of the S02 contained in these lines. The streams from lines 84 and 98 are passed into a gathering line 106 which leads to a dehydration zone 107. From time to time, it may be necessary to remove water from the S02 streams in lines 49, 61 and 73. In such a case, the streams from lines 49, 61 and 73 are passed through gathering line 111, valved line 112 and line 106 to dehydration zone 107.

The water from dehydrator 107 will contain acidic ma- 7 teriali and this solution is passed via lines=11 and" 93 to tlie decompositionvessel 8U;

The dehydrated streamfrom zone 1073's passed through l'in'el lfi to a'purifi'cation zone 1 17. Normally thestreams in: lines 49,- 61* and 73 pass directiy by way ofi line 11 1, valved line 11 9 and line 11 6 tozone=1 1-7.' In-purifibation zone 1217, the S62 and H25 are separated; for example, by fractional liquefaction because of the spread between the boiling points of these compounds; From zone 117; theliquid S02 is recycled to the extraction system via lines 121 and 3I. The H'zS is-discarded-or'sent' to sulfur recovery byway of line 1 22'.

It should be understood that many details of; process technique have-been omitted inthe above specific embodiment of our process. Many variations thereon will sug: gest themselves to those-skilled in the art-andsuchexpedicuts are within the purview of the present invention.

We claim:

1% A process for refining a virginhydrocarbon distillate inthe heavier-than-gasoline range which contains objectionable amounts of organic-sulfur compounds and aromatic compounds, which process comprises contacting said distillate at a temperature below' about C. with a liquid treating agent consisting essentially of 14-500 volume percent of liquid S02, based onsaid distillate,,and an AlCla-hydrocarbon complex containingbetween about '2'5 and 75 wt. percent of AlCla, in an amount equal to between 0.5 and mols of AlCls per gram atom of sulfur in said distillate, separating a rafiinate phase from an extract phase comprising liquid treating agent, hydrocarbons and sulfur compounds, removing occluded and dissolvedtreating agent from said railinate phase to recover a product containing less sulfur and less aromatics than said distillate and treating said extract phase to recover S02.

2. The process of claim 1 wherein the temperature of contacting is belowabout C;

3. Theprocess of claim I wherein the amount of liquid S02 is between about and 100 volume percent.

' process of claim 1 wherein said complex cong comprises contacting said distillate with a liquid treating agent consisting essentially of liquid S02, about to 100' volume percent based on said distillate, and an AlClshydrocarbon complex which contains about wt. percent of A1613, in an amount equal to about 2- to 3 mols of A-lCls per gram atom of sulfur in said distillate, at a temperature. of contacting at about 20' (3., separating a; raflinate phase from an extract phase comprising liquid treating agent, hydrocarbons and sulfur compounds; removing occluded anddissolved treating agent from said rafiinate phase to recover a productoil of satisfactorily low'sulfur-content and of good burning quality, andtreat: ing said extract phase to recover S02 and the hydrocarbon and sulfur compounds therefrom.

References (Jited in the file of this patent vUISII 'IIED STATES PATENTS 1,550,523: Eichwald. Aug, 8, 1925 1,831,265 Schonberg- Nov. 10, 1931" 1,891,582 Morrell et al. Feb. 14, 1933 1,941,251 Davis Dec. 26,1933 2,091,978 McKittrick et al Aug. 24, 1931 2,106,234- Bray Jan. 25,1938 2,114,524 Egli Apr. 19,1938 2 ,257,086. Atwell Sept. 30, 1941; 2,260,279! D?Ouvil le et al Oct. 21, 194 11 2.4045921: Naragon July 23, 19.46 

1. A PROCESS FOR REFINING A VIRGIN HYDROCARBON DISTILLATE IN THE HEAVIER-THAN-GASOLINE RANGE WHICH CONTAINS OBJECTIONABLE AMOUNTS OF ORGANIC-SULFUR COMPOUNDS AND AROMATIC COMPOUNDS WHICH PROCESS COMPRISES CONTACTING SAID DISTILLATE AT A TEMPERATURE BELOW ABOUT 0* C. WITH A LIQUID TREATING AGENT CONSISTING ESSENTIALLY OF 14-500 VOLUME PERCENT OF LIQUID SO2, BASED ON SAID DISTILLATE, AND AN ALCL3-HYDROCARBON COMPLEX CONTAINING BETWEEN ABOUT 25 AND 75 WT. PERCENT OF ALCL3, IN AN AMOUNT EQUAL TO BETWEEN 0.5 AND 5 MOLS OF ALCL3 PER GRAM ATOM OF SULFUR IN SAID DISTILLATE, SEPARATING A RAFFINATE PHASE FROM AN EXTRACT PHASE COMPRISING LIQUID TREATING AGENT, HYDROCARBONS AND SULFUR COMPOUNDS, REMOVING OCCLUDED AND DISSOLVED TREATING AGENT FROM SAID RAFFINATE PHASE TO RECOVER A PRODUCT CONTAINING LESS SULFUR AND LESS AROMATICS THAN SAID DISTILLATE AND TREATING SAID EXTRACT PHASE TO RECOVER SO2. 